The present invention relates to a method and apparatus for monitoring the progress of labor during childbirth.
Normal labor is generally divided into three stages: The first stage begins with the onset of labor and ends when dilatation of the cervix is complete; the second stage begins at that point and ends with the complete birth of the baby; and this is followed by the third stage which ends with the delivery of the placenta. During labor it is common to use either an external ultrasonic system for recording the baby's heart rate, and an external system for detecting the mother's uterine contractions, or an electronic system to sense the baby's heart pulses by an electrode attached to the baby's head and the mother's contractions by a pressure catheter applied to the mother inside the uterus.
However, a number of other physiological conditions of the mother and baby during labor must also be monitored in order to determine the progress of labor. These additional conditions include: (1) effacement (the thinning out of the cervix that occurs before and during the first stage of labor); (2) cervical dilatation (the increase in size of the cervical opening); (3) position of the cervix (the relation of the cervix to the vaginal axis, normally the fetal head); and (4) station (the level of a predetermined point of the fetal presenting part with reference to the mother's pelvis). The more common determination of station is the distance between the tip of the fetal head and the ischial spines which can be palpable by the physician; but a more accurate determination of station is the distance between the bi-parietal diameter (BPD) of the fetal head and the mother's pelvic inlet.
The foregoing conditions are generally determined by a physical examination, i.e., by the insertion of a finger through the mother's vagina. However, the accuracy of such a "finger" examination is very subjective and depends to a great extent on the experience, judgment, and even finger size, of the physician. Other drawbacks in such a physical examination are that it can be done only at spaced intervals, it generally produces discomfort to the mother, and it involves a number of risks including contamination, infection, dislodgment of a fetal monitor, injury to the baby, etc. Failure to interpret the precise stage of the labor progress from the physical examination can result in injury or even death of the baby or of the mother.
Many devices have been proposed in the past for automatically monitoring these conditions. As examples, U.S. Pat. No. 4,476,871 proposes an elongated tube having electrodes spaced along its length to monitor cervical dilatation during labor; U.S. Pat. Nos. 4,942,882 and 5,135,006 propose a fetal monitor probe attached to the fetal head to monitor heart beat, which probe is calibrated to monitor progress of descent; U.S. Pat. No. 5,222,485 proposes an elongated inflatable sac to monitor the position of the fetus and the configuration of the cervix; and U.S. Pat. No. 5,406,961 proposes a pessary to monitor the configuration of the cervix. However, for one reason or another, none of the previously proposed devices has come into any widespread uses and the historical "finger" examination continues to be the one in common use to this day.